MESTINON

What it is

Mestinon contains pyridostigmine bromide as its active substance. Mestinon is a cholinergic antimyasthenic that works through competitive inhibition of the cholinesterase enzyme, which normally breaks down acetylcholine at cholinergic synapses and neuro-effector junctions.

Approved indications

— Myasthenia gravis.

Dosing overview

For myasthenia gravis, the standard dose is 1 to 3 tablets of 60 mg two to four times daily, with higher doses in severe cases. Alternatively, 1 to 3 Timespan tablets of 180 mg may be taken once or twice daily, with an interval of at least six hours between doses. Dosage and frequency depend on the patient's clinical response and may vary day to day according to disease remissions and exacerbations and physical or emotional stress, with larger doses timed to periods of greatest fatigue such as 30–45 minutes before meals in patients with difficulty eating.

Key safety warnings

Particular caution should be used in patients with epilepsy, bronchial asthma, bradycardia, recent coronary occlusion, vagotonia, hyperthyroidism, cardiac arrhythmias, or peptic ulcer. Large oral doses should be avoided in patients with megacolon or decreased gastrointestinal motility, as the drug may accumulate and cause toxicity when gastrointestinal motility is restored. Overdosage may result in cholinergic crisis and underdosage in myasthenic crisis. Care should be taken in counteracting side effects with atropine, as such use, by masking signs of overdosage, can lead to inadvertent induction of cholinergic crisis. Vital capacity should be routinely measured whenever dosage is increased to ensure good respiratory function, and adequate facilities for cardiopulmonary resuscitation, cardiac monitoring, endotracheal intubation, and assisting respiration should be available during dosage adjustment. Mestinon is mainly excreted unchanged by the kidney, and lower doses may be required in patients with renal disease, with treatment based on titration of drug dosage to effect.

Contraindications

Mestinon is contraindicated in patients with known hypersensitivity to anticholinesterase agents and bromide, and in those with intestinal and urinary obstruction of mechanical type.